I'm wondering about the best clock option for my xmega project. I've got no constraints, except the I want to use USB. From the USB design note AVR1017 I see that I need a 48Mhz clock that can be generate by the internal calibrated PLL. There is a mention that the internal DFLL can calibrate the PLL and no external crystal may be required.
I don't really see against what the DFLL will calibrate and I don't want to rely on manual calibration during manufacturing.
Should I design a crystal anyway ?
If yes, what frequency is best ?
What about using a 32kHz vs traditional 16Mhz, for example) ?